Martian Pāhoehoe Lava

This is a comparative study of inflated and disrupted pāhoehoe lava on Mars and the Earth. The project will involve fieldwork in the Zuni-Bandera Volcanic Field of New Mexico and mapping of potentially analogous lava flows within the Elysium region of Mars.

Pāhoehoe Lava on Mars and the Earth: A Comparative Study of Inflated and Disrupted Flows

What: This is a comparative study of inflated and disrupted pāhoehoe lava on Mars and the Earth. The project will involve fieldwork in the Zuni-Bandera Volcanic Field of New Mexico and mapping of potentially analogous lava flows within the Elysium region of Mars.

When:  July 8-August 5

Where:

  1. Department of Earth & Environment, Franklin & Marshall College, Lancaster, PA (main location).
  2. NASA-Goddard Space Flight Center, Greenbelt, Md (several day trips)
  3. Zuni-Bandera Volcanic Field, New Mexcio (~10 day trip to Zuni-Bandera Volcanic Field, NM to complete the fieldwork component of the project).

Who: 6 students and Professor Andy de Wet (Franklin & Marshall College), Dr Chris Hamilton (NASA-Goddard Space Flight Center) and Dr Jake Bleacher (NASA-Goddard Space Flight Center).

Project Overview and Goals

The goal of this project is to characterize disrupted pāhoehoe textures within basaltic sheet flows. To do so we will conduct 10 days of fieldwork in the Zuni-Bandera Volcanic Field (ZBVF), NM, where project faculty Chris Hamilton (NASA-GSFC) and Jake Bleacher (NASA-GSFC) have several years of field experience. Our previous work has involved a larger field team and focused largely on mapping the extent to which sheet inflation has occurred with the McCartys flow (in the ZBVF). That work produced numerous new questions about the details related to emplacing each sheet lobe, or plateau. We have previously stated that the locations of slabby pāhoehoe patches within a plateau appear to be random. Mapping the location and size of these patches as part of this study will enable us to assess if the spatial distribution is random or if it displays organized relationships with other features such as inflation pits or plateau margins, or if the slabby terrain might outline pathways along which the flow was concentrated in later stages of flow emplacement.

Upon identifying the location of slabby pāhoehoe patches we will systematically assess the dimensions of slabs. Slab thickness can be related to the cooling history of the flow by the equation:

t = 164.8C2

(Hon et al., 1994) where t is time in hours and C the crust thickness in meters. By measuring the thicknesses of slabs we can determine if a given patch has experienced more than one disruption event, and whether different areas of the sheet appear to have experienced one or more disruption events at similar times after the initiation of crust formation. Jake Bleacher has worked with Tim Orr (USGS, Hawaiian Volcanoes Observatory) to characterize one feature in the Bandera flow as a shatter ring. However, Orr has identified 14 additional features across the Bandera flow that are suspected to be shatter rings. Confirmation of several additional shatter rings would support the hypothesis that these features together outline a flow pathway, or tube, within the Bandera flow that was used to deliver lava to the flow front. Completion of all three field tasks will provide the students with a strong background in identification of disrupted pāhoehoe textures on Mars. Potential papers that might result from this work include 1) Mapping the location of the Bandera lava tube by identification of a chain of shatter rings, and 2) Characterization of inflation pulses within one sheet lobe of the McCartys flow, NM.

In addition to fieldwork in New Mexico, we will conduct lava flow facies mapping of lava flows within the Elysium region of Mars. There are many examples of features within a small portion of this flow field that are analogous to the Bandera and McCartys inflated and disrupted flows. This style of facies mapping is only now becoming possible due to the acquisition of images with the Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) at 6-12 m/pixel, and the High Resolution Imaging Science Experiment (HiRISE) at resolutions below 1 m/pixel. These images enable for the first time detailed mapping at a scale at which the textures and features that are indicative of lava inflation, and lava disruption can be discerned.

Chris Hamilton has extensive experience mapping this flow field (Hamilton et al., 2010, 2011), and has spent several years requesting targets within this area for the HiRISE team, many of which are now acquired and released to the public. In addition to mapping surface textures across the flow several specific features could be examined in detail as part of a student project. One example of possible features to be examined by students is enigmatic ringed pits. These features have been suggested to represent unique types of impact craters or features related to ice/volatile processes, although no detailed study has yet been conducted. However, they display many similarities with inflation pits as seen in the McCartys flow, or could also share a common formation process with terrestrial shatter rings. Similarly, students can examine the margins of the flow field for additional evidence of inflation clefts.

Broader goals include exposure to planetary geology, a greater appreciation of the role of NASA in planetary exploration and research, develop experience in doing original research, work together in a team of researchers with a common goal, exposure to research with a broad appeal and relevance.

One of the challenges of doing research on Mars is that everything is based on remote sensing, theoretical considerations, and analog studies. We are planning to take a 10-day trip to the Zuni-Bandera Volcanic Filed in New Mexico to directly observe and measure processes and features that are probably direct analogs to features the students will be mapping on Mars. Chris Hamilton and Jake Bleacher have extensive experience mapping at this location and know the area very well. We have clear goals for the fieldwork but we will also respond to the interests of the students in crafting specific projects.

We may visit the Air and Space Museum in Washington, which has an excellent planetary exhibition.

In addition to the Keck Symposium, we will explore the possibility of presenting the results of this research at LPSC in Houston or NE-GSA in Lancaster, PA in 2014.

Geologic Background

The morphologies of lava flows generated by effusive basaltic eruptions can provide a record of paleo-eruption conditions at the time of emplacement. Basalt, when in liquid form, is a Bingham fluid (opposed to a Newtonian fluid like water). However, as the flow cools its rheology will change, first to a viscoelastic material and then to a brittle solid. Generally, the cooling-induced increase in viscosity of a basalt flow during emplacement will increase the confining strength of its margins and tend to resist flow. However, depending on the eruption rate from the vent and local discharge rate through a lava pathway, lava flow velocities may be great enough to disrupt the surface crust. The balance between confining strength and internal stresses can produce a variety of flow surface textures over multiple scales. Basalts are commonly divided into pāhoehoe (smooth) and ʻaʻā (rough) textures. ʻAʻā tends to form when the viscosity and/or velocities of the flow are high because the associated shear stresses will tear the surface of the flow into breccia. The velocity profile across the surface of the flow will typically transport the breccia to the flow front and margins, thereby producing a channelized flow with a rough and spinose surface texture. In contrast, pāhoehoe textures form when a flow viscosity and/or local discharge rates are low enough that continuous deformation of the confining viscoelastic layer will prevent complete disintegration of the surface crust, thereby allowing lava to be transported through thermally insulated internal pathways located beneath a smooth crust, or in other words, the cracks and tears in the crust can be healed and a smooth surface is produced.

Earth Science studies of basaltic eruptions tend to focus on hazard assessment modeling, with the goal of predicting regions of lava inundation given a range of likely eruption parameters. In contrast, studies of martian lava flows are typically concerned with estimating eruptions parameters based on the characteristics of previously emplaced flows. In other words, terrestrial lava flow studies generally involve forward modeling, whereas martian studies are typically aimed at using similar models to “back out” the eruption conditions. The simple distinction between pāhoehoe and ʻaʻā end-members has generally been adequate for mapping flow fields with the goal of establishing basic models of flow emplacement, but there exist a range of intermediate flow types that defy such basic categorizations. Determining the characteristics and emplacement conditions associated with these transitional flow types therefore represents the next big step in terms of understanding the diversity of lava flow morphologies and modeling their emplacement processes and paleo-environmental significance on Earth and Mars.

Disrupted pāhoehoe is a term used to describe a rough basaltic texture (at the meter scale) that does not form in the same continuous manner as an ʻaʻā flow. This process occurs during catastrophic events that disrupt already cooled pāhoehoe crust through drastic changes in the eruption conditions at the vent or local discharge rates through the sudden release of lava stored within a segment of the lava pathway system (e.g., rupture of the confining margins of a perched lava pond). However, given that both ʻaʻā and disrupted pāhoehoe can be rough in a general sense it can be difficult to distinguish them in remote sensing imagery, which could lead to misinterpretations of lava flow type in remote locations on the Earth and on planetary surfaces such as Mars.

In this study, we will focus on characterization of disrupted pāhoehoe textures on flows in the Zuni-Bandera Volcanic Field (ZBVF), NM, to establish a context for interpreting the significance of analogous sheet-like flow units in the Elysium region of Mars. The ZBVF is composed of >100 monogenetic vents (low shields and cinder cones) from which their basaltic lava flows coalesce (Luedke and Smith, 1978; Luedke, 1993) to produce a “plains-style” (Greeley, 1982) volcanic province. Within the ZBVF a large number of basaltic volcanic features are well preserved (Nichols (1946). We plan to conduct field work on the Bandera and McCartys flows. The Bandera and McCartys flows are the two youngest flow fields in the ZBVF at 9.5-10.9 kyrs and 2.5-3.9 kyrs respectively.

The McCartys flow is characterized as a pāhoehoe sheet flow with sections of ʻaʻā. At the scale of 10s to 100s of meters, the flow comprises multiple topographic plateaus and depressions. Some depressions display level, smooth floors, while some are bowl shaped with floors covered in broken lava slabs. The boundaries between plateaus and depressions are also typically smooth surfaces that have been tilted to angles sometimes approaching vertical. The upper margin of these tilted surfaces displays large cracks, sometimes containing squeeze-ups. The bottom boundary with smooth floored depressions typically shows embayment by younger lavas. It appears that this style of terrain represents the emplacement of an extensive sheet that experiences inflation episodes within preferred regions where lateral spreading of the sheet is inhibited. Inflation involves hydraulic lifting of large sections of surface crust to accommodate increased volume of the liquid core. Depressions are often the result of non-inflation and can be clearly identified by lateral squeeze-outs along the pit walls that form when the rising crust exposes the still liquid core of the sheet. These areas form broad, elevated plateaus of generally smooth pāhoehoe lava. Within the sheet flow units we have identified locations of “slabby” pāhoehoe, which forms when the crust of an inflating sheet flow fractures during inflation, but does not become part of a laterally emplaced rubble unit. As such, slabby lavas typically form slabs for which the thickness relates to the amount of time that the crust had cooled prior to disruption. Because the region is covered by trees and shrubs, we have been unable to map the extent and distribution of slabby lava across an inflated plateau, nor have we systematically determined if these slabby sections comprise similar slab thicknesses, or a multi-modal distribution of thicknesses, which might suggest that the flow experienced multiple catastrophic pulses of increased eruption rate or local discharge rate.

The Bandera flow is characterized as an ʻaʻā and tube-fed pāhoehoe flow. The Bandera Tube is easily accessible within the El Malpais National Monument. However, in the distal sections of the flow field the traces of the tube (open roof sections and accessible drained tube areas) are lost within an extensive pāhoehoe sheet. However, this sheet displays numerous quasi-circular, rough patches that appear to be somewhat aligned in a pattern similar to open roof tube sections closer to the vent. These features are thought to represent shatter rings (Orr, 2010) as are seen in Hawaiʻi (Per. Com. Tim Orr, 2010), but have not been confirmed. Shatter rings form over lava tubes as changes in flux though the tube result in over pressurization and upheaval of the crust above the tube. As such, this feature is a form of disrupted pāhoehoe.

Volcanic plains on Mars are composed of lava flows and their morphologies provide information about changing eruption conditions on the planet through time. Elysium Mons and surrounding Elysium Planitia form the second largest volcanic province on Mars, after Tharsis. The ages of surficial volcanic plains units in this region span from the Hesperian to Amazonian (Tanaka et al., 2005) and include some of the youngest flows on the planet. In this study will focus on pahoehoe-like lava flow units identified in northeastern Elysium Planitia by Keszthelyi et al. (2010) and Hamilton et al. (2010, 2011). The region of interest covers ~30,000 km2 and includes a diverse range of lava flow morphologies related to lava flow inflation and surface disruption. Although few people have studied this flow unit in particular, the surrounding region includes several major outflow channels that are widely interpreted to have been carved by water during catastrophic aqueous outflow events (e.g., Plescia, 1990, 1993, 2003; Fuller and Head, 2002; Burr et al., 2002; Burr 2005; Burr and Parker, 2006). However, more recent studies have demonstrated that the surfaces of these outflow channels appear to be covered in lava (e.g., Jaeger et al., 2007, 2008, 2010; Hamilton et al. 2010c, 2011; Ryan and Christensen, 2012), which suggests that volcanic processes have played a role on the modification of these channels as well.

Careful examination of flow units in northeastern Elysium Planitia is therefore important for distinguishing between volcanic and aqueous flow origins. These hypotheses can be distinguished from one another by identifying landforms indicative of inflation and surface disruption, which are typical of lava flows, but not of aqueous flow deposits. Inflation refers to the process by which lava flows thicken through endogenous growth. This process is analogous to the inflation of a balloon in which incoming fluid is retained by a deformable layer that expands to accommodate the new volume. However, if the internal pressurize of the balloon exceeds its confining strength, then the balloon may rupture. In an analogous fashion, newly emplaced lava will cool and develop rheologic gradient along its margins that includes a brittle outer core, underlying viscoelastic layer, and fluidal (Bingham) core. The outermost layers may crack and continuously deform to produce inflation structures such as tumuli, lava-rise plateaus, inflation clefts, and lava-rise pits (Walker, 1991), but if the internal pressure suddenly increases due to sudden changes in local discharge rate, then the surface of lava may be disrupted into slabs and auto-brecciated rubble (Guilbaud et al., 2005). As such, disrupted pāhoehoe can be indicative of non-uniform emplacement rates, particularly at the local scale within a flow. Developing field experience to confidently identify these surface features in remote sensing data is therefore vital to determining the origin of flow units in Elysium Planitia and other volcanic regions of Mars.

Student Projects

The student projects will comprise three components: Component 1 will be the field work in the Zuni-Bandera Volcanic Field in New Mexico; Component 2, will be the mapping of volcanic features in the Elysium area of Mars; Component 3 will be the continuing research during the following academic year (access to ArcGIS required).

Component 1: Zuni-Bandera Volcanic Field mapping

The students will work in pairs to map various volcanic features in the Zuni-Bandera Volcanic Field. They will likely use a variety of techniques including detailed mapping using GPS (available from F&M and NASA). Depending on the particular interests of the students, samples may be collected and could be analyzed using the lab facilities at F&M (XRF, XRD, ICP etc).

Component 2, Mapping volcanic features in the Elysium area of Mars.

Our preference is to assign each student a separate area on Elysium. This is the region we know well and it will form the basis on which to expand our research efforts. This component will have the following goals and structure:

  1. Download, georeference and assemble the required datasets. We will be using a wide variety of datasets including MOLA (gridded data product), THEMIS, CTX and HiRISE data. We will use ArcGIS to build the required databases and compete the mapping and analysis.
  2. Recognize and develop criteria, and map the various morphological features associated with lava flows on Elysium.
  3. Measure various parameters such as aerial extent, surface texture, cross-sections etc.
  4. Describe and interpret these morphological features based on our understanding of geological processes on Mars.
  5. Compare these features to analog features on the earth (including observations made during the field work in New Mexico).
  6. Interpret the origin of these features.
  7. Place the formation of these features into the broader context of the geological evolution of Mars by mapping their boundaries to determine their relationship with other volcanic deposits.
  8. Develop the academic year part of the project.

Component 3: The follow-up academic year component of the project may take one of many forms:

  1. Complete the database begun over the summer. Continue the mapping of the volcanic features of Elysium, compare these observations to the features mapped in the Zuni-Bandera Volcanic Field (need access to the ArcGIS software).
  2. Complete a similar study in other areas of Mars and make comparisons to other terrestrial locations (for example Hawai’i).
  3. Come to conclusions about the competing interpretations of the origin of various landforms on Elysium, specifically whether they are lava flows or aqueous flow deposits or some combination of the two.
  4. Draw broader conclusions about the role of volcanic and fluvial processes in the evolution of Mars.

Logistics/Field Conditions

The project will start in New Mexico with 10 days of field work, we will then travel to Franklin & Marshall College, Lancaster Pa for the remainder of the project.

  • New Mexico: During the field work we will be based in Grants New Mexico and travel daily to the field sites. Accommodation will be in a motel (no camping). Expect the field work to be very physically demanding involving long days in rough terrain under hot, dry conditions (average July high temperature is 91oF). Students will be expected to bring there own field clothing and equipment including a backpack, sturdy boots (not sneakers!), water bottle, long pants, hat, and leather-palmed gloves. A camera and hand-held GPS would be helpful but specialized equipment such as high precision GPS units will be supplied by the project.
  • F&M: While in Lancaster the students will stay in college housing but will prepare their own food; computer and analytical lab work will be carried out in the Department of Earth & Environment.

Recommended Courses/Prerequisites (should have at least 2):

  • Geomorphology
  • Mineralogy and/or Petrology
  • Volcanology
  • GIS and Remote Sensing
  • Planetary Geology

References

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